Surface coated calcium carbonate pigments



suRFAcnco-A'mn cALcruM-cARBoNAr-E PIGMENTS Lawrence M. Liggett, Wyandotte,,Mich., assignor to Wyandotte Chemicals Corporation, Wyandotte, Mich., a corporation of Michigan 'No Drawing. Original application September 1, 1953,

Serial No. 377,983, .now. Patent 'No. 2,841,504, 7 dated July 1, 1958. Divided and this application (April 9, 1956, Serial No. 582,311

7 Claims. (Cl. 260-235) This invention wrclatesdo novel surface-coated calcium carbonate pigments whichhave improved properties as rubber reinforcing pigments. More specifically, the inn-alkylamines and rosin amines, and a second coating material selected from the group consisting of 10-.20carbon-atormfatty acids, .rosinacids, lower esterssoflrosin acids and alkali metal salts; ofrosin acids.

Calcium carbonate, particularly when in a finely 'divided state-of theorder of 0.1 micronorless, hasmany desirable properties which make it-valuab1e as: areinforcing pigment in both natural and synthetic rubbers. In particular, the fine particle size calcium carbonate reinforces the rubber in which his incorporated and gives rise to high tensile strengths in'the rubber stocks. Because calcium carbonate is pure whitein color, it is possible to prepare high ytensile strength light colored :rubber stocks, which is not possible with many reinforcing pigments such as carbon black. Yet another valuable property of calcium carbonateis thatit. develops good building tack in 6R4 formulations.

In spite of the many desirable properties of calcium carbonate, it has, certain seriouslshortcomings which limit its acceptance by the rubber industry; The .ultra fine :par-

Unitcd States Patent processed on conventional rubber equipment.

2,927,091 Patented Mar. 1, 1960 special detackifying agents are used. When high loadher, the resulting stocks are so sticky that they cannot be Obviously this characteristic limits the utility of calcium carbonate as a pigment in this type of polymer.

As. set forth in the copending application of Alfred Korejwact aL, Serial No. 363,916, filed lune 24, 1953,

.now .U.S. Patent .No. 2,7 09,160, rnany of the aforementioned shortcomings of calcium carbonate can be over come .by coating .the surface of "the calcium carbonate tively-low processing temperatures, which characteristic is known as scorchiness? in therubber art. The scorchiness.of such aminecoated calcium carbonate contain- I ing rubber stocksmequires-close'r andjrnore carefulc'ontrol of processing Ltemperatures than are normally employed in the rubber art. The extra care that is required has limited the acceptance of such amine-coated calcium carbonate pigments.

It is an objectofthis invention to provide a calcium carbonatepigment having improved processing characteristics andtone which is more easily dispersed in natural and synthetic rubbers.

A further objectof this invention is to provide a cal- .ciumcarbonate pigment that will prov-ideimproved physical properties in the rubber compositions in which it is incorporated.

Another object of the present invention is toprovide a calcium, carbonate pigment which will provide optimum teanresistance and tensile strength in natural rubber ticle size calcium carbonate forms hard agglomcratcs which are extremely diificult to incorporateand disperse in the rubber matrix: When such a fine particle size calcium carbonate is incorporated into rubber on a two-roll differential speed rubber mill, the calcium carbonate pigrnent terms a hard lcalceon the back roll which mustbe loosened by scraping, andtthe resulting agglomerated .particles disperse poorly in the rubber. The aforementioned difiiculties can be partially overcome by master batching techniques, ,but these require longer processing cyclesv and limit the acceptance of caloium carbonate in the rubber industry. A further shortcoming of calcium carbonate is that the 300% and 500% modulus values are lowerthan desired in many applications. Yet another shortcoming different pigment loadings and it is not possible to obtain both optimum tear and tensile values in the same rubber stock. In addition, both the optimum tear and tensile values are obtained at, pigment loadings outside of the preferred pigment loading ra ge that is employed in the rubber arts. Whereas calcium carbonate can be used over a wide range of, pigment loadings in both natural and the diene type synthetic rubbers, it canonly be .used

in relatively low loadings in butyl type polymers, unless Other objects and advantages of this invention will become apparent from the following detailed description thereof.

Ithas been discovered that a calcium carbonate pigment of excellent quality can be prepared by coating the surface of a finely divided calcium carbonate with both a higher amine selected from the group consisting er 10-18- carbon primary n-alkylamines and rosin amines (hereinafter referred to simply as the higher amine for the sake oftbrevity); and a second coating agent selected from the group consisting of 10-20 carbon fatty acids, rosin acids, lower esters of rosin acids and alkali metal salts of rosin acids. These novel surface-coated calcium carbonate pigments have excellent processihg characteristics and are easily incorporated into rubber stocks without the difficulties that are usually associated with such fine particle size calcium carbonate pigments.

' In addition to the improved processing characteristics,

the surface-coated calcium carbonate pigments impart proximately 50 part loadings, unless special detackifying agents are employed. I

The chemical structure and nature of the 10-18 carbon atom primary n-alkylamines are well known and need not be set forth in detail. Such amines are normally derived from fatty alcohols by reaction with ammonia. Although all of the 10-18 carbon atom primary n-alkylamines give excellent results, the 16-18 carbon atom amines give rise to especially outstandingproperties in the coated calcium carbonate and such pigments are a preferred embodiment of the invention. The rosin amines, as their name implies, are derived from wood and gum rosins. Chemically the rosins are 20 carbon atom organic acids, principally of the abietic and pimaric acid type. The rosin amines are prepared by first converting the rosin acid to its nitrile (by reaction with ammonia) and hydrogenating the rosin nitrile to form the corresponding amine. A thorough description of the many possible sources of rosin amines and methods of preparing same is contained in U.S. Patent 2,491,913, and that description is incorporated herein by reference. Any such rosin amine is operable in the present invention;

The 10-20 carbon atom fatty acids are well known and such acids as linoleic, myristic, oleic and stearic are operable in the present invention. The rosin acids that are'operable include those of the abietic-type and the pimaric-type. For a description of typical operable rosin acids see TAPPI Monograph Series No. 6, P169-173, published in l948'by the Technical Association of the Pulp and Paper Industry, 122 East 42nd Street, New York, New York. The term lower esters of rosin acids includes the esters of 4 carbon and lower alcohols such as the methyl, ethyl, isopropyl, butyl, ethylene glycol and diethylene glycol esters.

The quantity of treating agent that is incorporated on the surface of the calcium carbonate pigment lies Within the range of approximately 1-5%, although smaller or larger quantities may be employed if desired. While quantities of treating agent of less than 1.0% may be employed, the maximum improvements in properties are not obtained. Similarly, quantities of treating agent in excess of 5% may be employed and may further improve the processing characteristics of the pigment, but such improved processability is associated with a concomitant decrease in the physical properties of the rubber stock. The optimum combination of properties is usually obtained Within the range of 2.0-3.5% treating agent.

'In addition to the consideration of the total quantity of treating agent applied to the calcium carbonate, attention must be directed to the molar ratio of the higher amine and secondary treating agent that is employed. The molar ratio of the secondary treating agent to the higher amine should be at least 1/ 1, since the pigment will be scorchy if the ratio is reduced substantially below this value. This ratio may be as high as 5/1, or even higher, with optimum results usually being obtained at a molar ratio of approximately 3/1. Of course it is obvious that the optimum ratio will depend upon the particular amine and the particular secondary treating agent that are employed, but in general optimum results will be obtained within the above limits.

The novel surface-coated calcium carbonate pigments can be prepared in many different ways. For example, an amine salt of a fatty'acid, or other secondary treating agent, may be blended with a calcium carbonate pigment and the resulting mass hammermilled'or ball milled. Obviously, the calcium carbonate can be first hammermilled with the higher amine and then the secondary treating agent, or the order can be reversed. Alternatively, a calcium carbonate pigment can be treated with the higher amine in an aqueous slurry, as disclosed in the copending application of Alfred Korej'vva et al., Serial No. 363,916, filed June 24, 1953, now U.S. Patent No. 2,709,160, and the resulting amine-treated calcium carbonate then hammermille'd with the secondary treating agent. However, since the improved properties of the surface-coated pigments are largely dependent, at least in theory, upon obtaining a uniform coating on the pigment, it is preferred to surface-coat the calcium carbonate in an aqueous slurry that contains an emulsion of both the higher n-primary alkylamine and the secondary treating agent.

The following examples are set forth to more clearly illustrate the principle and practice of this invention to those skilled in the art.

EXAMPLE 1 This example illustrates the method of preparing a higher amineestearic acid coated calcium carbonate pigment by first preparing a higher amine-coated calcium carbonate in aqueous solution'in accordance with the method disclosed in the copending application of Alfred Korejwa et al., Serial No. 363,916, filed June 24, 1953, now U.S. Patent No. 2,709,160, and subsequently incorporating the stearic acid on the calcium carbonate by hammermilling.

The amine-coated calcium carbonate was prepared by reacting by-product liquor from a commercial ammoniasoda process plant and consisting of approximately 110-120 g.p.l. of CaCl solution (distiller blow-off liquor from the ammonia-soda process) with a solution of approximately 160-190 g;p.l. concentration of Na CO and -70 g.p.l. concentration of NaHCO (decomposer outlet liquor from the armnonia-soda process). As a factor in controlling the particlesize of the precipitated calcium carbonate, caustic soda was added to the distiller blow-oil liquorin sufiicient quantity to neutralize 80% V of the NaHcO content. An alkylamine, whose alkyl group contained 16-18 carbon atoms and was derived from .tallow, i.e. a mixture of n-priinary alkylamines commercially available under the trade name Armeen T manufactured by Armourand Company, Chicago, Illinois, in the form of a hydrochloric acid salt, was added to the calcium chloride solution or distiller blow-off liquor, in an amount of 0.5 percent by weight on the basis of equivalent CaCO precipitate derivabletherefrom. Stearic acid in an amount corresponding to 1.25% of the calcium carbonate, was then incorporated in the dried amine-treated calcium carbonate-and was thoroughly incorporated thereon by hammermilling. The resultant product contained 1.75% treating agent.

EXAMPLE 2 This example illustrates the method of preparing a higher amine-stearic acid coated calcium carbonate by first preparing an amine-coated calcium carbonate in accordance with the method of the copending application of Alfred Korejwa et al., Serial No. 363,916, filed June 24, 1953, now U.S. Patent No. 2,709,160 and treating the resulting product, While still in aqueous suspension, with stearic acid. An arnine-coated calciumcarbonate, the amine described in Example 1, was prepared as described in Example 1, with the single exception that the amine content was increased to 0.75%. Stearic acid, 1% based upon the dry weight of the calcium carbonate precipitate, was dissolved in acetone and added with stirring to an aqueous slurry of the amine-coated calcium carbonate. The resultant product contained 1.75% treating agent.

ageamoai EXAM PhE a This example illustrates the method (of preparing a, sni'facecoaterl calcium carbonate pigm ntby treating an aqueous slurry of the pigment with an emulsion containingboth a'higher amine and stearic acidl Sixteen grams of a 16-18 carbon primary n-alkylamine,

the amine described in Example 1, and 48 grams of stearic acid were melted together andaddedto .1200 .ml. ofboiling water containing 18.7 grams. oftriethanolamine as an emulsifying agent. This emulsion was then added with stirring to an aqueous slurry containing 3300 grams of calcium carbonate at a temperature of 140 F. The resultant product contained 2% treating agent.

EXAMPLE 4 In thisexampiean aqueous slurry of calcium carbonate l was treated first with an emulsion of a higher" and then with an emulsion of stearic acid.

Sixteen grams, as a' 10%"aqueous emulsion, of the amine described in Example 1 was added with stirring to an aqueous slurry containing'3300 grams of calcium carbonate at a temperature of 120 F. Thisslurry was filtered, wasjhed free or chloride ions and reslurried. emulsion of'stearic acid which contained 48.5 grams of stearicacid was then added to the slurry with stirring at a temperature of approximately 140 The slurry was then filtered and dried. The product contained 2% treating agent.

EXAMPLE 5 Example 3 was repeated except that lauric acid was used in lieu of Stearic acid.

EXAMPLE .6 Example 3 was repeated except that decylamine was used in lieu ofthe 16-18 carbon primary n-alkylamine.

EXAMPLE 7 Example 3 was repeated except that dodecylamine was se in lieu o he 6- ca bo P ma y nky EXAMPLE 8 Example 3 was repeated except that dehydroabielylamine was used in lieu of the 16-18 carbon primary nalkylamine.

i EXAMPLE 9 A calcium carbonate pigment was surfaced coated with one partdehydroabietylamine and three parts lauric acid following the procedure described in Example 3.

EXAMPLE 1o The processing characteristics of the surface-coated product of Example l were compared with the characteristics of an uncoated calcium carbonate of the same particle size by incorporating 200 parts of each pigment in 100 parts of natural rubber on a two roll differentialspeed rubber mill. Whereas the uncoated calcium carbonate formed a hard cake on the back roll, which cake had to be removed by scraping,.the surface-coated product showed only a slight tendency to cake and it was not necessary to scrape the back roll. Visual examination of the stock containing uncoated calcium carbonate revealed the presence of poorly dispersed pigment fagglornerates, whereas the surface-coated product as well dispersed and showed no such agglomerates.

The above-described master batches were employed in preparing the followingrubber composition:

Component: Parts Smoked sheet 100 Zinc oxide n 5 2,2 benzothiazyl disulfide (Altax) 1 Sulfur 3 Stearic acid 1 5 CaCO pigment 100 Only 3.75 parts used with snrfacetreated pigment.

6 was. w at h r newing P ysical p pertieswere obtained: 1

As seen frornthe above table, the stocks containing the surface-coated calcium carbonatehad superior modulus and tensile yaiues, as compared with the stock containing the uncoatedg calciurn carbonate. Thus, surface-coating of the caicium carbonate notonly improved the processing characteristics of.;the pigment, but improved its rubber reinforcing properties as well.

Similarly, the same surface-coated calcium carbonate was found to have superior processing characteristics in GRS, cold GRQS, neoprene and Butyl rubber.

EXAMPLE r1 The surface-coated calcium carbonate of Example 1 and an uncoated calcium carbonate control were incorporated into the following Butyl rubber formulation:

Component: Parts Butyl rubber Zinc oxide 5 Parafiin -1 -L, 2 Sulfur 2 Z-mercaptobenzothiazole (Captax) 0.5 Tetramethylthiuram disulfide M e t h yl Tuads) 1.0 CaCO pigment Q 7.5

After press curing at 307 F the following tensile values w r were Table I1 Uncoated Surface- Flime ofCure, Minutes, 307 F. GaCOi Coated Control 021003 The above data indicate that higher tensile .values are obtained in @Butyl rubber stocks with the surface-coated calcium carbonate pigments .of invention. Other physical properties such as elongation, hardness, etc. were substantially the same in both stocks.

S l d Bun b r star-k a B asted by ma ing the content of the surfacecoated calcium carbonate to 11 5 parts in tl e aboy enoted recipe. The stock han ne l i fthe mi l and co ld be eas ly Proc s d calender-s, and other common rubber processing equipment. 0n the other hand, when the uncoated calcium carbonate loading was increased to parts, the stock became so sticky that it would not be handled on the mill. Thus, by employing the surface-coated calcium carbonate pigment, it is possible to obtain much higher pigment loadings in Biltyl rubber stocks than were here to fore possible]. a

EXAMPLE 12 The surface-coated calcium carbonate pigment of Ex ".7 ample 1 and an uncoated calcium carbonate control were incorporated into the following cold GR-S formulation:

Component: 1 7 Parts GR-S (41.? F. polymer). 100 Cumar resin 20 Zinc oxide r 5 Stearic acid 1 2,2 benzothiazyl disulfide (TAltazd) V1.5 Diphenylguanidine 0.5 Sulfur 2.5 CaCO pigment 100 After press curing at 287 E, the following physical properties were obtained:

Table III Cure, Uncoated Surface Physical Property 287 F., 02100; Coated .Minutes control 0300;

Tensile 40 21550 21680 7 e 50 t 2,490 20 600 675 600% Modulus 50 750 From a consideration of the abovedata, it is seen that higher modulus and tensile values are obtained with the surface treated product. Elongation, hardness, tear resistance, etc., were equivalent in the two stocks.

EXAMPLE 13 Afer press curing at 287 F., the following properties were obtained:

Table IV Referring to the above tensile strength data, it will be noted that optimum, reinforcing properties are obtained in the range of approximately 40-60 parts loading. Similarly, optimum tear; resistance properties are obtained at approximately-the same range of pigment loading, viz. 50-75 parts. These properties are to be distinguished from uncoated calcium carbonate pigments where optimum tensile properties are obtained at ap proximately 25 parts loading and optimum tear resistance values are obtained only at greater than 100 part loadings. 1

These results are significant for two reasons: (1) it is possible to obtain both optimum tear and tensile values 15 in a single rubber stock with the surface-coated calcium carbonate, whereas this result cannot be obtained with the uncoated pigment, and (2) optimum values are obtained at approximately 50 parts loading, which loading is used extensively in the rubber industry.

EXAMPLE 14 To illustrate the elfect of coating agent content and the molar ratio of the second treating agent to the higher amine on the surface-coated calcium carbonate pigments,

several calcium carbonate pigments were surface-coated by the technique of Example 3 with aqueous emulsions containing the higher amine described in Example 1 and stearic acid. Both the total quantity of surface treating so agent applied and the molar ratio of the higher amine to stearic acid were varied. The surface-coated calcium carbonate pigments were then compounded into the following GR-S formulation;

Component: Parts Zinc oxide 5 4n Sulfur 2.5

Curnar resin 20 n-Cyclohexylbenzothiazyl S u l p h o n a mi d e (Santo'cure) 1.5 Tetramethylthiuram disulfide M e t h y l 45 Tuads) Y 0.5

Stearic acid H p 1.0

CaCO pigment 150 60 The ratios of the surface treating agents and the physical Tensile Strength, p.s.l. Pigment Loading' Cure Time, I

' Tear Resistance, p i Pigment Loading Cure Time,

Minutes:

anamorproperties of the vulcanizates are set forth in Table V below:

Talzl eV Surface-Coating Molar Rubber Physicals Ratio Run t Stearic ,No., Percent Percent Acid 300% 500% 'Amine Stearic Amine Modu- Modu- Tensile Tear Acid 3 his 1 lus treated Control 250 1, 075 1, 500 150 1.75 7/1 275 1,375 1,710 180 1.50 3/1 350 1,375 1,740 170 72.25 3/1 1 35 1,475.1 1,680 145 1.5 l/1 4.00 1,570 160 It will be noted from the. above data, that each and every surface-coated pigment gave improved modulus and tensile values in the vulcanizate. The eifect of the molar ratio of'the secondary treating agent to the higher amine is seen in the 300% modulus values. As the stearic acid/higher amine ratio is decreased, i.e. as the proportion of amine is increased, the modulus values increase. The increase in modulus is accompanied by an increase in the scorchiness of the pigment, however, and experience has shown that the .best combination of properties is obtained when the molar ratio of the secondary treating agent to the higher amine does not exceed 7/1 and preferably when the ratio isabout 3/1.

EXAMPLE .15

To illustrate the variation that can be made in the secondary treating agent, Example 2 was repeated except that" the 1% stearic acid was. replaced with, respectively, the methyl ester of abietic acid, the diethylene glycol ester of abietic acid, the triethylene glycol ester of abietic acid, the sodium salt of abietic acid and tall oil (a commercial product comprising 70% rosin acids and 30% fatty acids, chiefly oleic and linoleic). Eachof the surface-coated pigments was then incorporated into the following natural rubber stocks:

Component: Parts Smoked sheet 100 Zinc oxide 5 Stearic acid 3 Sulfur i l 3 2,2 benzothiazyl disulfide (Altax) 1 CaCO; pigment 100 Each of the pigments had greatly improved processing characteristics, and when press cured at 260 F; had the following physical properties:

Table 1 VI Rubber Physicals Secondary Treating Agent 300% 500% Tensile Modulus Modulus Untreated Control"; 325 1,150 a, 010 625 1, 800 2, 040 at 600 l, 625 2, 920 Triethylene ester of Ahietic Acid 550 1, 625 2, 800 Sodium Salt Abietic Acid .1 575 1, 675 2, 8. 0 Tall Oil 1 a. 525 1, 575 2, 940

1 Commercial Inixture70% rosin acids, 30% fatty acids, chiefly oleic andlinoleic.

As noted from the above table, each of the treated pigments had superior modulus values and comparable tensile values.

A similar group of coated pigments was prepared by Q reacting calcium chloride and sodium carbonate in an aqueous solution in which both the higher amine and the secondary treating agent were emulsified. The same proportionsof treating agents were employed and the calcium carbonate precipitate was coated in situ as it was a 10 prepared from the reacting solutions. In this case, even superior properties were obtained, probably because of a more homogeneous coating of; thecalcium carbonate par-' ticles. EXAMPL '16 The surface-coated calciumcarbonate pigment of Example 5 and an untreated control were incorporated into. the following natural rubber stock:

Component: Parts Smokedv sheet 10.0 Zinc oxide N i v 5 Stearic acid -a I 3 lfur v H a p 3 2,2 benzot-hiazyl disulfide (Altax) 1 i a --r-- The surface-coated pigment had notably superior processing characteristics When the two stocks were press cured at 260 F., the following physical properties were obtained:

Table VII Uncoated Surface- Physieal Property CaO 0a Coated Control OaOO;

300% Modulus 325 400 500% Modulus--. 1, 1,250 Tensile 1, 620 1,850

As noted from the above table, the surface-coated pigment had superior modulus and tensile values.

EXAMPLE 17 The surface-coated pigments of Examples 6 and 7, in which the higher amine employed was, respectively, decylamine and dodecylamine andin which the secondary treating agent was stearic aQ d, were incorporated into the rubber stock shown in Example 14. The following The above data demonstrated that the surface-coated pi m n s have supe modulu d a value EXAMPLE 18 The surface-coated pigment of Example ,8, in which the higher amine employed was dehydroabietylamine and in which the secondary treating agent was stearic acid, was incorporated into the natural rubber formulation dc scribed in Example 16. The following physical properties were obtained: t

, Table IX Rubber Physicals Pigment 300% 500% Tensile 'lear 20 921 411 Mod lu 600 ,60 23 M 7pc, 150 0 sass 4 20 The improvement in properties of the coated pigment are apparent from the above data. Comparable results '11 are obtained When the dehydroabietylamine is replaced with abietylamine. EXAMPLE 19 The surface-coated pigment of Example 9, in which the higher amineemployed was dehydroabietylamine and in which the secondary treating agent was lauric acid, was incorporated in the 6R4 formulation set forth in Example 14. The surface-coated pigment had superior processing properties, as compared with an uncoated control. The surface coating also improved the rubber rcinforcing properties, since a 500% modulus value of 1150 psi. was obtained in the vulcanizate.

While the novel surface-coated calcium carbonate pigments of the present invention have been discussed prineipally in relation to their utility as a rubber reinforcing pigment, the novel pigments of this invention are valuable for use in paper coating, surface-coating compositions, printing inks, etc. In particular, the surface-coated caloium carbonate pigments of the present invention contain a much smaller proportion of larger agglomerated particles (screened residue) than uncoated calcium carbonates having the same particle size. This fact is illustrated by the example belowr EXAMPLE 20 The proportion of agglomerated particles contained in two of the surface-coated calcium carbonate pigments of Example 13 and an uncoated calcium carbonate control are determined as follows:

. Ten gram portions of dry calcium carbonate samples were mixed with 180 ml. of water and 20 ml. of a 1% solution of sodium kerylbenzenesulfonate wetting agent. This mixture was stirred for five minutes and then washed through a 3-5 mesh screen for 8 minutes with tap water. The amount remaining on the screen was dried and weighed. The percentage of residual solid product remaining on the screen, on the basis of the. original 10 gram amount, thereby indicated the proportion of the relatively large size agglomerated particles in the original product. The results of this residue test are set forth below:

Table X Surface Coating Percent Percent Percent 325 Mesh ine Stearic Residue Acid UncoatedControl 18.7 0.75 2.25 2.7 0.25 1. 75 1. 4

The foregoing results, indicating an extremely low percentage of relatively large size agglomerated particles in the surface-coated calcium carbonate of the present invention, render such product especially advantageous as a paint and printing ink pigment where the presence of oversized particles is likely to produce the defect known in such arts as grainine'ss.

Throughout the specification and claims the pigments of the invention are described as having dispersed on their surface both a higher amine and a secondary treating agent. When the secondary treating agent is an acid, obviously a reaction will take place with the amine to form a salt.

This application is a division of my copending application, Serial No. 377,983, filed September 1, 1953, Patent No. 2,841,504, for Surface Coated Calcium Carbonate Pigments, which copending application is a continuationin-part of application, Serial No. 325,883, filed December 13, 1952, now abandoned, for Surface Coated Cal cium Carbonate Pigment, which latter application is now abandoned.

What is claimed is:

l. A rubber composition comprising a conjugated di-' olefin elastomer having dispersed therein 7.5 to 200 parts by weight of a surface-coated calcium carbonate pigment per parts by weight of said elastomer, said pigment having dispersed on the surface thereof sufi'icient surfacetreating agent to materially improve the rubber processing and rubber reinforcing properties thereof; said surface-treating agent consisting of (1) a higher amine selected from the group consisting of primary n-alkylamines whose alkyl groups contain 10-18 carbon atoms and rosin amines, and (2) a second treating agent selected from the group consisting of 10-20 carbon atom fatty acids, rosin acids, lower esters of rosin acids and metallic salts of rosin acids, the molar ratio of the second treating agent to the higher amine being at least 1/ 1.

2. A rubber composition comprising a conjugated diolefin elastomer having dispersed therein 7.5 to 200 parts by Weight of a surface-coated calcium carbonate pigment per 100 parts byweight of said elastomer, said pigment having dispersed on the surface thereof 1.05.0% by weight, based upon the weight of said pigment, of a surface-treating agent consisting of (1) a higher amine selected from the group consisting of primary n-alkylamines whose alkyl groups contain 10-18 carbon atoms and rosin amines, and (2) a second treating agent selected from the group consisting of 10-20 carbon atom fatty acids, rosin acids, lower esters of rosin acids and metallic salts of rosin acids, the molar ratio of the second treating agent to the higher amine being at least 1/ 1.

3. A rubber composition comprising a conjugated diolefin elastomer having dispersed therein 7.5 to 200 parts by weight of a surface-coated calcium carbonate pigment er 100 parts by weight of said elastomer, said pigment having dispersed on the surface thereof 1.05.0% by weight, based upon the weight of said pigment, of a surface-treating agent consisting of (1) a higher primary n-alkylamine whose alkyl group contains 16l8 carbon atoms and (2) a second treating agent consisting of a 10-20 carbon atom fatty acid, the molar ratio of the fatty acid to the primary n-alkylamine being at least 1/-1.

4. A rubber composition comprising a conjugated diolefin elastomer having dispersed therein 7.5 to 200 parts by weight of a surface-coated calcium carbonate pigment per 100 parts by weight of said elastomer, said pigment having dispersed on the surface thereof 1.05.0% by weight, based upon the weight of said pigment, of a surface-treating agent consisting of (l) a higher primary n-alkylamine whose 'alkyl group contains 16-18 carbon atoms and (2) stearic acid, the molar ratio of the stearic acid to the primary n-alkylamine being at least 1/1-.

5. A rubber composition comprising a conjugated diolefin elastomer having dispersed therein 7.5 to 200 parts by weight of a surface-coated calcium carbonate pigment per 100 parts by weight of said elastomer, said pigment having dispersed on the surface thereof 1.05.0% by Weight, 'based upon. the weight of said pigment, of a surface-treating agent consisting of (l) a higher primary n-alkylamine whose alkyl group contains 16-18 carbon atoms and (2) lauric acid, the molar ratio of the lauric acid to the primary u-alkylamine being at least l/ l.

6. A rubber composition comprising a conjugated di' 7. A rubber composition comprising a conjugated diolefin elastomer having dispersed therein 7.5 to 200 parts by weight of a surfacewoated calcium carbonate pigment,

,and (2) stearic acid, the molar ratio of the steaxic acid to the dehydroabietylamine being at least 1/ 1.

References Cited in the file of this patent UNITED STATES PATENTS 2,274,521 2,663,695 Perlofi et a1 Dec. 22, 1953 Berry Feb. 24, 1942 14 2,709,160 Korejwa et a1 May 24, 1955 FOREIGN PATENTS 293,164 Italy e- Febf13, 1932 OTHER REFERENCES Davis and Blake: Chemistry and Technology of Rubber, p. 746, Reynolds Publishing Co., 1937. (Copy in Scientific Library.)

Morris et al.: Ind. and Eng. Chem, vol. 40, No. 12, 7 December 1948, pages 2325-2333. 

1. A RUBBER COMPOSITION COMPRISING A CONJUGATED DIOLEFIN ELASTOMER HAVING DISPERSED THEREIN 7.5 TO 200 PARTS BY WEIGHT OF A SURFACE-COATED CALCIUM CARBONATE PIGMENT PER 100 PARTS BY WEIGHT OF SAID ELASTOMER, SAID PIGMENT HAVING DISPERSED ON THE SURFACE THEREOF SUFFICIENT SURFACETREATING AGENT TO MATERIALLY IMPROVE THE RUBBER PROCESSING AND RUBBER REINFORCING PROPERTIES THEREOF, SAID SURFACE-TREATING AGENT CONSISTING OF (1) A HIGHER AMINE SELECTED FROM THE GROUP CONSISTING OF PRIMARY N-ALKYLAMINES WHOSE ALKYL GROUPS CONTAIN 10-18 CARBON ATOMS AND ROSIN AMINES, AND (2) A SECOND TREATING AGENT SELECTED FROM THE GROUP CONSISTING OF 10-20 CARBON ATOM FATTY ACIDS, ROSIN ACIDS, LOWER ESTERS OF ROSIN ACIDS AND METALLIC SALTS OF ROSIN ACIDS, THE MOLAR RATIO OF THE SECOND TREATING AGENT TO THE HIGHER AMINE BEING AT LEAST 1/1. 